Study On The Synthesis And Optical Properties Of Metal Oxide Semiconductor Nanomaterials

Nanometer scale semiconductor materials have been studied extensively in recent years because of their important applications in photovoltaic cell, sensing, optical emission and photocatalysis. Titanium dioxide is widely known to be the best photocatalyst due to its chemical stability, low cost and no toxicity. Since it act only by UV irradiation at around 360 nm region (Eg=3.2ev for anatase), so we have focused on T1O2 nanocrystallites to improved the utilization ration of visible light and increase the surface area.ZnO is a wide direct band gap (3.27eV) semiconductor, it can emit photons of UV light and broad visible spectrum, in order to get strong violet-blue emission, we investigated ZnO nanocrystallites doped with metal and nonmetal ions, and nanocrystallites composite. Here,it mainly contains 6 parts as follows: l.Nanoparticles of TiO₂ powder co-doped with La and N were prepared using a coprecipitation method followed by being two hours calcinated at a temperature ranging from 500 to 600℃ in NH₃/Ar atmosphere. Uniformly co-doped TiO₂nanocrystalline was 5-15 nm with surface area 65-125 m²/g. Optical absorption along with the microstructural investigation for monodoped and co-doped catalyst provided that a part of O vacancy of Ti₅O₉ was occupied by N, which is responsible for the band-gap narrowing of TiO₂, while La³⁺ doping prevents the aggregation of powder in process of nitrification. Superior catalytic activity was observed in the co-doped TiO₂ under visible light (350<λ<450 nm). 20 mg/l methyl orange solution could be docomposed completely within 1h using the 0.5 at.% La³⁺ doped TiO₂ calcinated in NH₃ for 2h.2.TiO₂ nanotubes were prepared by treatment of TiO₂ nanocrystallites in mild hytrothermal conditions in alkaline solution, then calcined at 400℃ in air and 500℃ in NH₃/Ar atmosphere. TiO₂ nanotubes were characterized by HRTEM,XRD and UV-Vis spructra. It shows that the nanotubes possess a layered structure and the tubeaxis is determined to be along (010) direction of the anatase phase. The formation mechanism of the nanotubes can be explained as folded sheets with a t^TiaC^ structure. The UV-Vis spectra shows a strong absorption in 260 nm.3. ZnO nanocrystallines doped with Cu2+ , Mn2+ and Cr3+ have been obtained by chemical precipitation from homogeneous solution ,respectively.Their emission properties have been researched for the first time.The results indicate that the red light emission are significantly quenched and blue-green light emission are strongly enhanced. The luminescence characteristics and corresponding mechanism for doped ZnO are reviewed.4.ZnO nanoparticles doped with nitrogen on surface were prepared by calcinating pure ZnO nanoparticles at 550°Cand 600°C in NH3 atmosphere. Uniform N-doped ZnO nanocrystal was characterized by TEM, XRD and XPS. A Strong violet photoluminescence at 400nm was observed at room temperature when excited with 300nm light, and the emission peak increases with the increase of nitrogen atoms concentration. The violet PL originated from the electron transition from shallow donor levels of oxygen vacancies and doping nitrogen atoms to the top of valence band level.5.ZnO nanorods were prepared by hydrothermal synthesis using Zn(OH)42" precursor in alcohol solution without and with the assistant of dodecyl benzene sulfonic acid sodium salt DBS or ethylenediamine at 110°C and 180°C. The microstructure of samples was studied by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED). The results show that single crystalline ZnO nanorods grow from ZnO nuclei spontaneously, and +c-axis ((001) direction) is the fast growth direction. This landing mode predominant in decreasing the high interfacial free energy caused by high symmetry of the (001) faces. The effect of the surfaces were discussed. Photoluminescence (PL) spectrum at room-temperature shows a UV emission near 400nm, which is likely related to the emission of high concentration excitons; and a yellow-green light emission at 550nm, which is related to defects in the rods.6. A ZnO/PANI composite nanoparticles has been synthesized using a simplechemical method. The TEM,XRD, UV-Vis and fluorescence spectra were used to characterized the composite nanoparticles. It shows that the ZnO/PANI possess "core-shell" structure. A dramatic increase in the luminescence intensity in the emission wavelength have been observed from the composite,company with the strong blue emission, the red emission decreased rapidly.